Method and optical drive for detecting a header region on an optical carrier

Abstract

The present invention relates to a method of detecting a header region for a writeable optical carrier. The method initially obtains a data signal (RF) from the optical carrier, and performs a low pass filtering the data signal (RF) for a pre-determined time constant. Subsequently, there is performed a comparison between the low pass filtered data signal (LPF_RF) and a dynamically determined threshold level (RF_th), whereby a positive indication of a header region (I, II, III) is obtained, if the low pass filtered data signal (LPF_RF) is above the dynamically determined threshold level (RF_th). In an advantageous embodiment, there is further performed a comparison of a polarity signal (DPII) to a previous polarity signal (DPI) so as to provide an indication of a land-groove transition. The present invention provides a simple and robust method of detection and header region and possibly a land-groove transition compared to the hitherto known solutions.

Description

FIELD OF THE INVENTION[0001]The present invention relates to a method of detecting a header region for a writeable optical carrier. Such optical carriers may in particular include a digital versatile disc of the read access memory format (DVD-RAM). The invention also relates to a corresponding optical drive.BACKGROUND OF THE INVENTION[0002]Optical storage of information on optical carriers or disks such as CDs, DVDs, HD-DVDs and BDs is being increasingly used in more and more applications. The corresponding demand for higher and higher information density (information per area) has given rise to a multitude of different technologies, each technology with various associated advantages and problems.[0003]Conventionally, the information on the optical carrier is arranged in spiral-like tracks with the information being grouped in blocks, each block having sectors with a header section, a data section, and an error correction code (eec) section. The header section typically contains inf...

AI Technical Summary

Benefits of technology

[0015]The invention is particularly, but not exclusively, advantageous for obtaining a stable and robust method of detection of a header region because the threshold level is dynamically determined, i.e. the threshold level may be adjusted depending on various parameters such as the RF amplitude itself, the reading speed, the clock frequency, etc. Furthermore, the method has the benefit that there is no immediate need to decode the information stored in the header region in order to detect the header region. Thus, if e.g. the focus settings of the optical drive are not optimized, for example during start-up or interruptions, it is nevertheless possible to detect a header region by application of the present invention.

[0021]This embodiment is particularly but not exclusively advantageous for obtaining an indication that a land-groove transition has taken place when passing a header region at a substantially unchanged radial distance on the optical carrier in a simple and very effective manner by utilizing the push-pull signal from the current and previous header region. Similarly to the header detection method there is also no need to decode any information stored in the header regions in order to obtain an indication of a land-groove transition. This may be advantageous under non-optimal settings of readout from the optical carrier in the optical drive.

[0022]Beneficially, at least one of the above steps may be performed in the digital domain in order to ease processing of the method. Additionally, the data signal may be averaged prior to being low pass filtered so as to obtain a more stable signal.

Problems solved by technology

This method suffers from the disadvantage that the first and second threshold levels must be set in advance, i.e. during the design phase or by calibration under manufacturing.

Therefore this method may yield incorrect header signals if for some reason the DPD levels at the header region are inappropriate for detection with this method.

This may be the case if there is beam landing, as this will give an offset error to the DPD signal.

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